This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 11(1999)-262603 filed on Sep. 16, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a motor. More particularly, the present invention pertains to a DC brush motor used as a driving source in applications such as a vehicular window regulator, power operated seat, and ABS (anti-skid brake system).
The axial dimension of a DC brush motor depends on the length of the armature made up of a coil winding and a core, the length of the brush or commutator, the length of the bearing, and the gaps that are required between adjacent members forming the motor. FIG. 11 illustrates an arrangement which makes it possible to shorten the axial length of a DC brush motor. In this motor construction, the out put side of a shaft 61 is supported in a rotatable fashion with respect to a casing 62 and a cover 73 by way of respective bearings 63a, 63b. The bearing 63b and a commutator 65 are positioned at opposite sides of an armature 64. To shorten the axial length of the DC brush motor, the bearing 63b and a portion of the commutator 65 are placed inside a coil winding 66 of the armature 64. A brush 67 and a brush supporting member 68 are disposed between one end of the armature 64 and the output side cover 73.
FIG. 12 illustrates a motor similar to that disclosed in Japanese Patent Laid-Open Publication No. Hei. 10 (1998)-248225. In this motor, a commutator 65 is disposed inside an armature 64 and a brush 67 is disposed inside the armature 64 so as to be movable in parallel with a shaft 61. The brush 67 is accommodated within a plurality of brush holders 68b which project in the axial direction of the armature 64 toward a disc-shaped main body 68a. The brush 67 is urged by a spring 69 to be in contact with a contact portion 65a of the commutator 65a. 
FIG. 13 illustrates another motor similar to that disclosed in Japanese Patent Laid-Open Publication No. Hei. 10 (1998)-174360. This electric motor is used as a driving source for an automotive ABS system. The motor includes a shaft 61 having opposite ends rotatably supported by respective bearings 63a, 63b. 
An output transmitting member 70 is positioned at a side of the bearing 63a, and a bearing 72 is provided on the output transmitting member 70 for converting rotational movement of the shaft 61 into reciprocating movement of a plunger 71.
With the motor construction shown in FIG. 11, the motor still possesses an axial length necessary for accommodating the brush 67 and the brush supporting member 68, thus making it difficult to make the motor smaller or thinner.
With the motor construction shown in FIG. 12, although the commutator 65 and the brush 67 can be inside the range defined or limited by the axial length of the armature 64, the bearing 63a cannot be placed inside the armature 64 due to the existence of the disc-shaped main body 68a between the bearing 63a and the brush 67. As a result, limitations are placed on the ability to make the motor smaller. In addition, with this structure, the contact portion or segment 65a is sector-shaped and is placed at just the outer side of the shaft 61 which is a narrow portion, thus making it quite difficult if not impossible to establish a sufficient area of the segment 65a, resulting in higher brush current density and thereby raising a problem which increases the brush friction.
With the structure shown in FIG. 13, the bearing 72 is placed next to the inside of the bearing 63a so that the flexing of the shaft 61 is lessened when compared to placing the bearing 72 next to the outside of the bearing 63a. However, in this construction, the bearing 72 has to be isolated from the bearing 63b in such a manner that the difference between the two bearings is greater than the sum of the axial lengths of the armature 64 and the commutator. As a result, the span between the bearings 63b, 72 is relatively larger, and so a problem arises in that the vibration reduction effect associated with the reduced flexing of the shaft 61 becomes insufficient.
The present invention provides a DC brush motor that includes an armature having a recessed or concave portion, a pair of bearings rotatably supporting the armature, a brush and a commutator. The brush, the commutator, and one of the bearings located nearer to the brush is accommodated in the recessed portion of the armature so as to be axially positioned within the axial length range of the armature. The axial length of the motor is thus shorter than that of a motor constructed so that the bearings, the brush, and the commutator are positioned outside the armature.
According to another aspect of the invention, a DC brush motor includes an armature, a commutator rotatable together with the armature, and having a brush contact portion oriented in the radially inward direction, and a brush extending in the radially outward direction to contact the brush contact portion of the commutator. With this construction, the accommodating portion in which the brush is accommodated is shorter in the axial extent as compared to a construction in which the brush is positioned to be movable in the axial direction of the armature.
According to a further aspect of the invention, A DC brush motor includes an armature having a cup-shaped or concave portion, a pair of bearings rotatably supporting the armature, and a commutator rotatable together with the armature. The commutator has a brush contact portion oriented radially inwardly, and a brush extends radially outwardly to contact the brush contact portion of the commutator. The brush, the commutator, and one of the bearings located nearer to the brush are accommodated in the cup-shaped or concave portion of the armature so as to be axially positioned within the axial length range of the armature.
The bearings located farther from the brush is at least partly accommodated in the armature so that the bearing located farther from the brush is axially located at least partly in the axial length range of the armature. The core of the armature can be in the form of a molding made of soft magnetic powder material. This increases the flexibility in design of the core shape as compared to an armature made of stacked iron plates (steel plates). In addition, the core possesses improved specific resistance compared to the stacked core, thus lowering the eddy current loss considerably and improving the motor efficiency.
The armature includes a shaft supported by the bearings, wherein the shaft has an eccentric portion formed on an output shaft portion. The eccentric portion is provided with a transmission bearing to transmit rotational movement of the output shaft portion to a driving portion which reciprocates. When the output shaft portion rotates, the resulting rotation is transmitted by way of the transmission bearing mounted on the eccentric portion of the output shaft portion to the driving portion to causes reciprocating movement of the driving portion. Due to the relatively short span between the pair of bearings supporting the shaft of the armature, the flexing of the shaft is relatively small when a radial force is applied to the shaft by way of the transmission bearing. In addition, the transmission bearing is placed inside the bearing which supports the armature. This reduces the flexing of the shaft when a radial force is applied to the shaft by way of the transmission bearing.